The present invention relates, in general, to method and apparatus for heating metal articles of nonmagnetic material to an elevated processing or forging temperature.
In the metal forging art, the customary methods heretofore employed for heating metal billets or workpieces of nonmagnetic material such as brass or copper to their forging temperatures of around 1500.degree. F. has been by the use of either a gas-fired or an electrically heated furnace in which the billets are heated. In these prior heating methods, however, the nonmagnetic material of the billets is subjected to the high (1500.degree. F.) furnace temperature for the entire time that they are within the confines of the furnace. As a result, the nonmagnetic billets encounter objectionable surface degradation or grain coarsening due to the extended period of time they are exposed to the high furnace temperatures.
Although such surface degradation or grain coarsening of the nonmagnetic billets could be substantially eliminated or greatly minimized by the use of induction heating to heat the billets to their forging temperature of approximately 1500.degree. F., such inductive heating of the billets is considerably less efficient than a high efficiency electric radiant heat furnace such as the slot-type furnace disclosed, for example, in U.S. Pat. No. 4,159,415 to Williams. Normal efficiencies of induction heating of articles of brass or other nonmagnetic metal materials is in the order of 30% to 35%, whereas the normal efficiency of heating such articles in a slot-type high efficiency electric radiant heat type furnace is in excess of 60%. For this reason, therefore, the heating of nonmagnetic metal billets to their forging temperature entirely by an inductive heating process has proven economically unfeasible.